Recently, SUV (Sport Utility Vehicle) has drawn attention as multipurpose passenger vehicle. SUV has features such as a large body securing a large interior space for achieving both sportiveness and practicability, and a high output engine mounted thereon for securing high maneuverability and high running performance. As a pneumatic radial tire for such SUV, used is an ultra-low profile pneumatic radial tire having a large tire outer diameter for achieving a high driving force, and also having an aspect ratio of 55% or less for achieving a high driveability.
As a tire for SUV with such features, Patent Document 1 discloses a tire having an aspect ratio of 55% or less and a large tire outer diameter of 750 to 820 mm, as well as having a two-ply structure including a high turned-up ply and a semi turned-up ply as carcass layers. The high turned-up ply is formed so as to extend each of both end portions of a carcass layer folded back around bead cores to the inner side of the ends of a belt layer. The semi turned-up ply is formed so as to extend each of both end portions of other carcass layer to a region between an end of the belt layer and a portion of the tire maximum width.
However, consider the case where a tire with an increased tire outer diameter as described above is provided with the two-ply carcass structure including the high turned-up ply having a folded length extending to both end portions of the belt layer and the semi turned-up ply having a folded length extending beyond the portion of the tire maximum width. The tire increases the weight significantly, so that the fuel consumption is inevitably increased. Accordingly, it is necessary to reduce the weight of the tire in order to suppress such increase in fuel consumption.
However, consider a single ply structure composed of only the high turned-up ply which is formed by omitting the semi turned-up ply from the above two-ply carcass structure in order to reduce the weight of the tire. In this case, if the tire has a large structure having an aspect ratio of 55% or less and a tire outer diameter of 720 mm or more, a share of a load to the carcass layer becomes too large. Accordingly, the load durability of the tire is deteriorated. Particularly, a stress is concentrated on the carcass layer in a vicinity of an outer end of the bead filler in the tire radial direction, thus bringing about a problem that the carcass layer is likely broken.
[Paten Document 1] Japanese patent application Kokai Publication No. 2004-352174